Plasma reforming

Hydrogen can also be produced by the direct thermolysis or thermocatalytic decomposition ( cracking ) of methane or other hydrocarbons. The energy requirement per mole of methane is in fact less than that for steam reforming (although only half as much hydrogen is produced) and the process is simpler. 

In addition, a useful by-product - clean solid carbon in the form of soot is produced. Obviously, this can be captured and stored more easily than gaseous carbon dioxide. Whereas thermocatalytic cracking offers the benefit of operating at a much lower temperature than direct thermolysis, it does suffer from progressive catalyst deactivation through carbon build-up. Moreover, reactivation would result in unwanted emissions of carbon dioxide. 

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Simplified schematics of a thermal plasma reformer for the production of synthesis gas from hydrocarbons. 1 = Anode, 2 = cathode, 3 = discharge, and 4 = insulator. 

Simplified schematics of a gliding arc-type plasma reformer. 1 = Electrodes, 2 = discharges, 3 = vessel with insulation, and 4 = electrode connectors. 

The plasma reformer efficiency reached 12.3% and 26% in gasoline auto thermal and steam reforming regimes, respectively. The typical composition of the effluent gas from the reformer operating in steam reforming mode was (vol%) H2—28.7, CO—15, C02—3, and CH4—40. 

The plasma decomposition process is applicable to any hydrocarbon fuel, from methane to heavy hydrocarbons. Similar to oxidative plasma reforming, plasma decomposition processes fall into two major categories thermal and nonthermal plasma systems. 

Schematics of thermal plasma reformer for decomposition of methane to hydrogen and carbon. 1 = Thermal plasma reactor, 2 = graphite electrodes, and 3 = hydrogen-carbon separation unit (cyclone).

Bromberg, L. et al., Plasma reforming of methane, Energy Fuels, 12,11,1998. 

Seguichi, H. and Mori, Y., Steam plasma reforming using microwave discharge, Thin Solid Films, 435, 44,2003. 

Since pyrolysis converts waste into CO, CH4, and H2, the product gases can be processed in an atmospheric pressure non-equilibrium plasma reformer to improve the energy-recovery potential of the product gas. Energy-recovery options include heat and chemical energy recovery. 

Figure 35 H2 yields (moles of H2lmole of i-Cg) at different reactor temperatures for various experimental configurations used in non-thermal plasma reforming of i-Cg. Maximum H2 yield from i-Cg is nine as shown by dashed line (Reprintedfrom Sobacchi et alfi copyright (2002), with permission from Elsevier)...

Very high temperatures (>3 000°C) are generated inside the plasma-arc reforming units. The energy, which is generated inside the plasma reformer, is not dependent on the chemical reaction. 

Plasma reforming of natural gas is attractive in that solid carbon is formed rather than carbon dioxide. The drawbacks are that the process requires substantial amoimts of electricity and, obviously, no advantage is taken of the energy that, otherwise, would have been obtained from the combustion of carbon. In terms of energy efficiency, therefore, it does not appear to be a very promising candidate. 

Plasma reforming of methane can be efficiently used to produce hydrogen-rich gas (50-75% H2, 25-50% CO) [le). Methane has also been converted to higher hydrocarbons (including ethylene and acetylene) by a microwave plasma [If], Heating induces important transformations not only in alkanes, but also in aromatic hydrocarbons, for example [Ig] ... 

BROMBERG, L., Hydrogen Production from Plasma Reforming, World Wide Web, http //www.eren.doe.gov/hydrogen/hyplsma3.htm, US Department of Energy (1997). 

Table 10-5. Composition of Products of Plasma Reforming of Unrefined Soybean Oil with and without Additional Catalytic Stage (0 C ratio 1.08)...

Barni, R. Quintini, A. Piselli, M. Riccardi, C. (2009). Experimental study of hydrogen plasma reforming by intermittent spark discharges. Journal of Applied. Physics, Vol. 103, pp. 063302.1-9... 

Benilov and Naidis performed numerical calculations for partial oxidation of octane in a plasma reformer [88]. They revealed that the reformer should be operatedatahigh 0/C ratio of 1.3-1.5 to maximise the hydrogen yield. In this instance the electrical discharge served more as an ignition source for the homogeneous partial oxidation reaction. With 0.045 kWh m hydrogen, the electrical power input was rather low. 

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